In the current state of technology, there has been an increased demand for devices with high power density. The requirements for devices such as microwave- and millimeter-wave devices, for example, are becoming increasingly stringent. To accommodate such demands, high-voltage gallium arsenide technology has been used with favorable results. Problematic, however, is the heat output attendant with increasing voltages.
There have been several approaches for dealing with the increased heat output experienced with high-voltage devices. In one approach, a handle material (e.g., a handle wafer) is bonded to a frontside of an active epitaxial structure, while the backside of the epitaxial structure is composed of a low-thermal-conductivity substrate (e.g., a gallium arsenide substrate). The substrate may be ground away and in its place a high-thermal-conductivity material may be bonded. The handle material may be removed, resulting in the epitaxial structure being formed on the high-thermal-conductivity material instead of the original low-thermal-conductivity substrate. Although this approach may result in a device better able to sink the heat output, the complexity of the process may be undesirable.
In another approach, the active epitaxial structure is simply formed on the high-thermal-conductivity material instead of on the low-thermal-conductivity substrate. Although this approach is less complex than one using an intermediate handle material, it may result in an inferior device due to the lattice mismatch between the epitaxial structure and the high-thermal-conductivity substrate.